共查询到20条相似文献,搜索用时 15 毫秒
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Y.Qiao Department of Civil Engineering University of Akron Akron OH - USA 《材料科学技术学报》2005,21(3):338-342
Due to the non-uniform nature of crack advance, when a cleavage front encounters a high-angle grain boundary, instead of simultaneous break-through along the whole boundary, the front transmission mode can be irregular, which results in a higher fracture resistance and a tortuous percolation behavior. In this paper, this phenomenon is studied quantitatively through the analysis on the work of separation and the change in strain energy for an Fe-3 wt pct Si alloy. The influences of the crystallographic misorientations, the break-through mode, the cleavage front profile, and the grain boundary properties are discussed in detail. 相似文献
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M.Abou Zied 《材料科学技术学报》2006,22(5):605-610
Microstructure and mechanical properties of ball-milled Al-8 wt pct Ni ribbon have been investigated by X-ray diffraction (XRD) and continuous Vickers hardness test, respectively. The results indicate that, the main phases of this alloy are α-Al and orthorhombic-Al3Ni. The lattice parameter of α-Al increases with increasing milling time. From the elastic constant of Al, the average contrast factors of the (111), (200), (220), (311) and (222) Bragg's reflections for pure edge and pure screw dislocations in fcc crystals with α/2〈110〉{111} slip system were calculated. The average grain size and dislocation parameters as a function Of milling time have been investigated using the modified Williamson-Hall plot and the Warren-Averbach equation, respectively.An attempt has been made to correlate the micro-hardness of milled ribbon with their grain size through the Hall-Patch relationship:HV0.01 = 742.45 〈 D 〉^-1/2 +401.55 (kg/mm^2). 相似文献
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Dongrong Liu ) Dianzhong Li) Baoguang Sang) ) Institute of Metal Research Chinese Academy of Sciences Shenyang China ) School of Materials Science Engineering Harbin University of Science Technology Harbin China 《材料科学技术学报》2009,25(4)
Macrosegregation in Fe-0.8 wt pct C alloy solidifying with equiaxed morphology was numerically simulated.Based on a two-phase volumetric averaging approach,heat transfer,melt convection,composition distribution,nucleation and grain evolution on the system scale were described.A weak-coupling numerical procedure was designed to solve conservation equations.Simulations were conducted to study the effects of cooling rate and nuclei density on the macrosegregation pattern.The relative influence of thermal buoya... 相似文献
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研究了直流电场作用下Al Si共晶凝固组织的变化。试验结果表明:电场作用改变了共晶Si的生长形态,随着电流密度的增加,共晶Si的形态经历一次细化的过程。初步分析了电场作用造成上述结果的机理。 相似文献
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直流电场对Al-Cu共晶合金凝固组织的影响 总被引:1,自引:1,他引:1
研究了直流电场作用下Al-Cu共晶凝固组织的变化.结果表明:电场作用改变了共晶晶粒尺寸和片层间距,随着电流密度的增加共晶晶粒尺寸和片层间距都经历了一次先细化后粗化的过程.初步分析了电场作用造成上述结果的机理. 相似文献
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针对稀土元素Eu对共晶硅有良好的变质效果,本工作研究了不同Eu含量(0.04%、0.1%、0.16%、0.22%,质量分数,下同)、冷却速率、变质温度、保温时间以及重熔次数对Al-7Si中共晶硅的变质效果的影响.结果表明:冷却速率的提高有利于Eu元素对光晶硅的变质,冷却速率越高,共晶硅由针片状完全转变为纤维状所需加入的Eu越少;变质温度和保温时间会影响Eu元素对共晶硅的变质效果,最佳的变质温度为750℃,最佳的保温时间为15 min;重熔次数的增多,将致使变质失效,在不影响稀土Eu变质效果的情况下,重熔次数应不超过三次. 相似文献
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Rongchang ZENG Enhou HAN Wei KE 《材料科学技术学报》2007,23(3):353-358
The corrosion morphologies of aged magnesium alloy AZ80 were investigated by immersion corrosion tests, scanning electron microscopy (SEM), electrochemical measurement. The T5 heat treatment was carried out in a vacuum furnace, holding for 16 h at 177℃, and then cooling in air. The results showed intergranular corrosion (IGC) occurred as an aged AZ80 sample was immersed in 3.5 wt pct NaCI aqueous solution for 1 h and the narrow path attack progressed predominantly along the bulk β phase in the grain boundaries or took place in the eutectic areas. IGC was attributed to the network distribution of β phase along the grain boundaries, the depleted aluminium in the precipitation areas and the breakdown potential. 相似文献
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采用金属铸造法制备过共晶Al-22Si合金试样块,在光学显微镜上观察细化变质后过共晶Al-22Si合金的微观组织形貌,并测试其布氏硬度值和铣削表面粗糙度.通过正交试验探究轴向切深、进给量、铣刀转速对铣削力的影响.实验结果表明:细化变质后的过共晶Al-22Si合金初晶硅尺寸减小,共晶硅呈短棒状,合金硬度很高,铣削表面粗糙度较小;在铣削加工中,铣刀转速对合金铣削力的影响最大,其次是轴向切深,最小的是进给量. 相似文献
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H.B.DongDepartment of Engineering University of Leicester Leicester LE RH UK 《材料科学技术学报》2005,21(5):753-758
1.IntroductionNumerical simulation of solute microsegregationhas become increasingly popular over the last severaldecades.The effects of solute back diffusion[1,2],den-drite coarsening[3],tip undercooling[4,5]and variation ofequilibrium data at the solid/liquid(S/L)interface[6~8]on the microsegregation have been investigated in vari-ous segregation models.In these models,dendrites arerepresented in spherical,cylindrical or plate-like geome-tries.During calculation the whole dendrite surface w… 相似文献
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Studies on the crystallographic growth habit of primary silicon crystals in an Al-16 wt% Si alloy were carried out by X-ray micro focus Laue analysis and ECP (electron channelling pattern) analysis. The plate-like primary silicon crystals grow by the same mechanism as that for germanium dendrites, i.e. the TPRE (twin plane re-entrant edges) mechanism. The spherical primary silicon crystal in sodium treated melts is composed of several pyramidal grains with tops at the centre of the sphere. Many of these grains have a twin relation to each other. The sodium enriched regions are found at the boundaries of these pyramidal silicon grains. The external surfaces of the spherical primary crystals exhibit regular crystal facets. The surface facets are most frequently parallel to {111} plane but there are also some facets parallel to other less densely packed planes such as {100}, {211} and so on. 相似文献
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强磁场下Zn-2 wt.%Cu合金定向凝固的初步研究 总被引:1,自引:0,他引:1
本文进行了10T强磁场下Zn-2wt.%Cu合金的定向凝固的初步研究.结果发现下拉速度较低时,无磁场时晶体以平界面方式生长,而施加磁场则产生带状组织,并且随着磁场的增加带状组织越来越明显,带状组织间距越来越小;当定向凝固速度较高,晶体以枝晶方式生长时,磁场促进枝晶的分枝,并扰乱枝晶规则生长;随定向凝固速度提高,磁场的作用逐渐减弱. 相似文献
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用SEM考察了生长速度R=30~2500μm/s时Al-12.7%Si共晶中硅相的形态与分枝特征。对深腐蚀样品的观察表明,共晶硅相具有连续生长、成束分布特征,随生长速度R增大,共晶硅逐渐由粗大片状向片状、条状转变。硅相生长与分枝特征与局部生长条件密切相关,从整体上看,随生长速度增大,晶体学生长与分枝特征减弱。 相似文献
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A rapidly solidified Al-17Si alloy was pre-pared by the ultrasonic gas atomization andextrusion method.Its superplasticity was studiedunder constant cross-head speed tensile test condi-tion over the temperature range of 450℃ to 550℃and strain rate range of 1.67×10~(-4) to 6.17×10~(-2) s~(-1).The superplastic behaviour of theas-extruded and the thermomechanically treatedsamples was compared.It was found that thethermomechanical treatment was essential toachieving superplastic deformation.A maximumelongation of 445% was obtained at test tempera-ture of 550℃ and strain rate of 6.17×10~(-4) s~(-1).The microstructures before and after deformationwere studied using OM,SEM and TEM.Void for-mation on the primary Si phase interfaces wasfound to have detrimental effect on superplasticity.It was also noted that the primary Si phasecoarsened rapidly during superplastic deformation.The micromechanisms of superplasticity,phasecoarsening and void formation were discussed. 相似文献
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The interaction of grain size and precipitation strengthening has been studied in a Ti-8 wt % Al-0.25 wt %Si alloy. Grain sizes varying from 9 to 90m were produced by warm-working and annealing the alloy in the single--phase field. A uniform distribution of the coherent
2 particles in the matrix was produced by ageing the alloy in the two-phase ( +
2) field. The yield strength Hall-Petch slopes of the alloys with and without the 2 precipitates were found to be nearly equal, indicating that the precipitation and grain-boundary strengthening are linearly additive. While specimens containing no precipitates exhibited a high ductility for all grain sizes, the ductility of the specimens with the
2 particles decreased drastically with increasing grain size. TEM examination of the specimens containing the precipitates revealed a highly planar, localized slip and SEM examination of the fracture surfaces of these specimens revealed a transition in fracture behaviour from highly dimpled to mixed cleavage and intergranular with increasing grain size. 相似文献
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目的 研究热处理条件下共晶层片组织的失稳机制,通过理论建模定量阐明控制层片失稳的关键因素。方法 以Al-Cu共晶合金为研究对象,采用铜模激冷的方法使合金发生激冷快速凝固,获得2个不同冷却速率下的细化共晶层片组织,进一步对所制备的样品进行不同温度及时间的退火处理。研究了退火条件下层片组织的失稳行为,进一步建立了层片失稳的理论解析模型,并基于模型,阐明了热处理条件下共晶层片失稳的机制。结果 凝固冷速为63 K/s和28 K/s的2个样品层片组织均发生了失稳,且在相同退火温度下,冷速为63 K/s的样品(初始共晶层片更细小)更易发生失稳,当退火温度及时间相同时,冷速为63 K/s的样品层片失稳程度更高。结论 在退火条件下,受瑞利不稳定性的影响,共晶层片失稳遵循由层片组织转为棒状组织、棒状组织转变为粒状组织的演变规律;层片厚度和退火温度是层片粒化的主要影响因素。 相似文献
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Filamentary preforms of aluminium-13 wt % Si alloy reinforced with TiC-coated carbon fibres were obtained by liquid metal infiltration using K2ZrF6 as wetting agent. The interfacial structure was investigated using analytical electron microscopy (TEM, SEM) and the fibre strength measured following each step of processing. The reaction between the K2ZrF6 deposit and the molten alloy is discussed on the basis of the reaction products formed at the fibre-matrix interface, which mainly consisted of fluoride compounds (K3AlF6), different zirconium-rich suicides (Si2Zr, SiZr (Al), (Al, Si)2Zr) and crystalline -alumina. Large amounts and/or inhomogeneous distributions of the K2ZrF6 deposit should be avoided, because the massive precipitation of colonies of intermetallics around fibres is conducive for the formation of harmful aluminium carbides and favours brittle fracture of the composite. The utilization of TiC-coatings formed by the reactive chemical vapour deposition process gave satisfactory results, both in terms of composite elaboration and fibre protection during liquid infiltration. 相似文献